In a gravity type of railroad classification yard, it is common practice to utilize wheel gripping car retarders at both master and group locations to control the leaving speeds of humped railway cars or vehicles. In addition, it is also becoming increasingly popular to employ a car retarder at the exit end of each of the class tracks of the yard to stop the oncoming railway cars as they are processed into the respective classification tracks. The car retarders frictionally engage or grip the opposite sides of the car wheels to slow down the moving vehicles as they pass through the master and group locations and to stop the railway vehicles at the exit ends of the class tracks. In many cases the frictional gripping action between the brake shoes and wheels causes extremely loud and piercing squealing noises to permeate the immediate surrounding residential area bordering the yard. These high pitched screeching sounds not only are irritating or annoying to residents of the area but also are painful and injurious to working personnel in the yard. In some cases, a partial or total loss of hearing may result when yard employees are exposed to the retarder noises for extended periods of time. It has been found that long-term exposure to sounds above a critical level adversely affects workmen or supervisory personnel who work in the area of the car retarders. These acute and detrimental sound waves are produced by the stick-slip or rubbing action which takes place between the sides of the wheels of the moving car and the engaging surfaces of the brake shoes of the actuated car retarder. In actual operation, it has been found that the most troublesome pitch or frequency range of the retarder generated sound waves lies between 2,000 to 4,000 hertz. Further, the loudness or amplitude level of the noises may reach a 130 decibels db(A) or more at a distance of 8 feet or less from the car retarder. Otolarynologists, audiologists and other qualified specialists have found that human beings experience discomfort and pain when exposed to noise levels of 120 db(A) or more and that repeated exposure to such high levels of noise can eventually result in hearing losses. Recently there have been numerous proposals and schemes to eliminate or at least reduce the noise level in order to comply with the regulations of the Occupational Safety and Hazard Act and the noise pollution ordinances of the given locale. However, each of these previous attempts was either prohibitively expensive or mechanically unsound and, therefore, did not meet with industry-wide acceptance. The proposition of replacing steel brake shoes with ductile iron appeared plausible but proved uneconomical since ductile iron shoes wear four times as fast as steel. Hence, a railroad car retarder equipped with ductile iron shoes normally requires four times as many shoe replacements as an all steel retarder. Obviously, a car retarder fitted with ductile iron shoes needs a greater number of adjustments and requires more periods of maintenance than a car retarder equipped with steel shoes. The use of lubricants, such as, oils and mixtures of other unctuous liquids, that are sprayed or otherwise applied to the contacting surfaces of the brake shoes and wheels for eliminating wheel squealing or screeching noises is also possessed of several shortcomings. The utilization of lubricants not only materially decreases the effective braking length of the car retarder but also dramatically increases the initial purchase price as well as the subsequent maintenance cost of the overall car retarder. A further deleterious effect of employing lubricants in combating the noise pollution problem is the unctuous ground covering in the immediate area of the car retarder as well as the oil dropping pollution caused throughout the classification yard. A further method in attempting to resolve the noise pollution problem in classification yards has been the erection of sound barriers or walls on the respective sides of the railroad car retarder. In previous types of noise barriers, the use of porous noise absorption material was unacceptable in that they soon become relatively ineffective in suppressing the noise produced by the car retarder. The principal reason for the loss in sound attenuation resides in the fact that the porous material readily becomes clogged with foreign matter, such as, dirt, oil, grease, water, ice and the like, which is common in a classification yard environment. In addition, low density types of noise absorption materials are generally susceptible to rapid deterioration due to the adverse physical and climatic conditions which are present in railroad yard milieu. Further, it will be appreciated that the maximum theoretical value of noise reduction or attenuation provided by a barrier structure is approximately 25 db which in many cases is insufficient to conform with the noise abatement ordinances in the particular locale and the safety standards set forth in the Occupational Safety Hazard Act of 1970. In present classification yards and in future proposed yard locations, it has been found that even at substantial distances, 5,000 feet or more, the noise level that permeates the area beyond the boundry line of the yard is in excess of the maximum permissible amplitude set forth in many of the local noise abatement ordinances. Thus, there is a vital need for providing an efficient noise reduction arrangement for effectively reducing or eliminating wheel squealing or screeching sounds produced by railroad car retarders. In addition, wheel squealing noises are produced at other locations in the trackway, such as, at curves or at tight gauge track sections where abrasive or rubbing action takes place between the wheels and the running rails. Hence, it is highly advantageous to provide an effective noise suppression arrangement for mitigating wheel screeching noises on curved track sections and at tight gauge locations.